1. Field of the Invention
The present invention relates to a device for detecting an abnormality in a pressure detector in an internal combustion engine.
2. Description of the Prior Art
Various methods are used for controlling an internal combustion engine for an automotive vehicle. These include minimum spark advance angle control for best torque (MBT), control of the lean limit of the air-fuel ratio, knocking control, and the like. Various sensors are necessary to carry out the above control methods, and each of these methods uses a pressure sensor for sensing the combustion pressure in the engine, and a piezoelectric type pressure sensor is considered most suitable for this purpose.
The operation of a piezoelectric type pressure sensor is based on the phenomena wherein an electric charge is produced in response to the application of pressure.
When a piezoelectric pressure sensor is used in a high humidity atmosphere, the insulation resistance of the piezoelectric pressure element is reduced, and hence the output of the piezoelectric pressure sensor is reduced. Also, when the connection terminal or the cable of a piezoelectric pressure sensor is contaminated, the output of the piezoelectric pressure sensor is reduced. In addition, if there is a break in a connection related to a piezoelectric pressure sensor, the sensor is brought to an open state.
Hence, in any method for controlling the internal combustion engine wherein a piezoelectric pressure sensor is used, it is necessary to be able to detect any abnormality in the piezoelectric pressure sensor, i.e., a reduction of output or an open state. However, a satisfactory method or device for detecting abnormality in a piezoelectric pressure sensor has not been obtained as yet.